The Queen arrived shortly after 5pm and stayed for 50 minutes. She smiled broadly at photographers as she got into her waiting Bentley.

Half an hour into her visit she was joined by the Duke of York, who drove himself to the hospital in his Range Rover. He left after an hour, saying his father was "mending well, thank you very much".

Prince Philip was taken ill at Windsor Castle on Monday afternoon, 24 hours after he had stood on the deck of the royal barge, Spirit of Chartwell, in wind and rain throughout the Thames Diamond Jubilee Pageant.

Doctors have said his bladder infection could have been brought on by his arduous afternoon, when he did not drink any fluids for several hours.

He was well enough to go carriage driving on Monday morning, but began feeling unwell when he got back and was taken to hospital in an ambulance, meaning he missed the Jubilee celebrations on Monday and Tuesday.

A short statement from Buckingham Palace, issued at 12.15 today, said: "The Duke of Edinburgh’s condition has improved considerably since coming into hospital on Monday. The treatment of his infection continues with antibiotics.

"He is likely to remain in hospital over the next few days. He is in good spirits."

Yesterday the Earl of Wessex said after visiting his father in hospital that he had been well enough to watch the Jubilee celebrations on television.

Earlier it was business as usual for the Queen as she got straight back into her normal routine of official engagements.

She attended a lunch of Commonwealth leaders at Marlborough House on The Mall, having earlier unveiled a portrait of herself.

Other members of the Royal family were also back to work - the Prince of Wales opened a sheep show in Scotland, the Duke of Cambridge was on his way back to his RAF Search and Rescue squadron on Anglesey and Prince Harry returned to his Army Air Corps Apache helicopter unit.